The development of single needle, disposable blood collection systems has provided a safe, relatively inexpensive and accepted modality for collecting units of whole blood from volunteer donors. Such units of whole blood are usually centrifugally separated into various therapeutic components, such as red blood cells, platelets, and plasma, for transfusion. Such systems have made possible large-scale collection of whole blood from volunteer donors at sites such as church halls, schools or offices remote from medical facilities. The availability whole blood collection systems suitable for volunteer donors is important, because it provides access to a relatively large pool of healthy individuals from which to draw needed supplies of whole blood components for life-saving or therapeutic purposes.
The conventional whole blood collection systems, familiar to and accepted by volunteer donors, can be used to collect plasma, as just described. However, such systems, by design, yield only a single unit of plasma per donor. Furthermore, such systems, by design, also take red blood cells from the donor. The donor must internally replace red blood cells before he or she can donate again. This replacement process takes six to twelve weeks, during which time the donor cannot give blood. Thus, such conventional whole blood collection systems are not suited for collecting the relatively large pools of plasma (called "source plasma") from which the various therapeutic plasma proteins, such as albumin and AHF (anti-hemophilic factor) are obtained by fractionation.
Therefore, the collection of source plasma from volunteer donors, as opposed to the collection of whole blood, is not widespread. As a result, much of the source plasma now collected comes from paid donors, not volunteer donors. It would be desirable to make the collection of source plasma a volunteer-based activity to a much greater extent than it is currently.
Various methods are known for the collection of source plasma (also called plasmapheresis). For example, using a modification of the above-described whole blood collection system, a unit of whole blood is collected and separated by centrifugation into red blood cells and plasma. The plasma is retained, while the red blood cells are immediately returned to the donor. The process is then repeated, collecting another unit of plasma and returning another unit of red blood cells. The result is the collection of two units of plasma for fractionation purposes. Because red blood cells are returned to the donor, this process allows more frequent donation, often as frequently as once per week. However, this process is time-consuming and, in part for this reason, does not appeal to volunteer donors. Furthermore, during the process, while the whole blood is being separated into red blood cells and plasma, the blood collection system (typically a series of integrally attached bags) is physically separated from the donor. Such physical separation requires procedures to minimize the risk of error when several donors are being processed simultaneously that one donor's red blood cells are not inadvertently returned to another donor. In addition, physical separation of the blood from the donor potentially raise concerns in the collection staff of exposure to infectious agents in the collected blood if fluid drips or leaks occur.
On-line extracorporeal separation systems, in which the blood collection system is not physically separated from the donor during the collection procedure, are also known. These can be either batch or continuous systems. Such systems employ either centrifugal separators or membrane filters.
A centrifuge-based system is disclosed in Judson et al. U.S. Pat. No. 3,655,123 entitled "Continuous Flow Blood Separator." The system of the Judson et al. patent was two needles, an outflow needle and a inflow needle. Whole blood is drawn from a donor via the outflow needle. The whole blood fills a buffer bag. Blood from the buffer bag drains, under the force of gravity into a centrifuge. The system of the Judson et al. patent uses the centrifuge to separate blood components. The plasma can be collected in a container. The red blood cells can be returned to the donor via the inflow needle.
A membrane-based system is disclosed in Popovich et al., U.S. Pat. No. 4,191,182.
The systems of the Judson et al. and Popovich et al. patents require an external source of electrical energy. Further, the systems rely upon a variety of mechanical components, including pumps and the centrifuge that prevent it from being readily portable.
Systems that include pumps are often constant volume systems, in which a relatively constant volume of fluid is pumped through the system per unit of time. Constant volume pumping systems suffer from the disadvantage that sudden over pressure conditions can occur if one of the fluid flow lines becomes crimped or is partly closed. These over pressure conditions are particularly undesirable in on-line extracorporeal blood separation systems, in which the fluid system of the blood separation device is in flow communication with the donor's blood circulation system.
The known extracorporeal separation systems therefore tend to be expensive, complex, not always "donor friendly", and generally unsuited for portable operation.
One system of membrane collection suitable for portable operation has been described in a published European Patent Application, Publication No. 0114698 published Aug. 1, 1984; entitled "Process and Apparatus for Obtaining Blood Plasma." In this system, a unit of blood is withdrawn from a donor into a set containing a membrane filter, tubing and a sterile blood receptacle. The whole blood is first passed through the filter. The plasma flows through the membrane filter and is collected in a separate plasma container. The remainder of the blood unit, which had passed from the inlet to the outlet of the filter, is accumulated in the sterile container such as a standard blood bag. It can then be immediately returned to the donor.
In this approach, the pressure available for driving the filtration process and for propelling the blood from the inlet to the outlet of the filter is relatively small. This pressure includes the donor's venous pressure (with an inflatable cuff, being on the order of 40 mm Hg) and available hydrostatic head (approximately 50 mm Hg) for a total pressure on the order of 90 mm Hg. These pressures may vary from donor to donor and from site to site. This can result in a relatively slow and variable plasma collection time. It also requires relatively large filters to function at the available low driving pressures. It can also be difficult to achieve precise anticoagulant flow proportional to blood flow with inexpensive and simple-to-use hardware.
Another membrane-based system is disclosed in a group of three U.S. Pat. No. 4,479,760 entitled "Actuator Apparatus for a Prepackaged Fluid Processing Module Having Pump and Valve Elements Operable in Response to Applied Pressures"; U.S. Pat. No. 4,479,761 entitled "Actuator Apparatus for a Prepackaged Fluid Processing Module Having Pump and Valve Elements Operable in Response to Externally Applied Pressures"; and U.S. Pat. No. 4,479,762 entitled "Prepackaged Fluid Processing Module Having Pump and Valve Elements Operable in Response to Applied Pressures," all issued to Bilstad et al. The system of the Bilstad et al. patents utilizes a disposable module containing a hollow membrane filter, a plasma container and other elements. A fixture is provided to receive the module during the donation cycle. Constant volume pumps in the fixture are provided to draw whole blood from the donor into the inlet side of the filter and to return the concentrated red cells to the donor from the outlet side of the filter. A single needle is used from both drawing the whole blood from the donor and returning concentrated red blood cells to the donor.
The system of the Bilstad et al. patents requires an exterior source of electrical energy. In addition, the fixtures can be relatively expensive and complex.
Thus there still continues to be a need for pumping systems providing substantially more pressure than gravity-fed systems, but without the potential of undesirable over pressure conditions. Such improved pumping systems would find particular application in the field of blood component collection, especially if such systems were also simple to operate and capable of easy transport.